In recent years, there have been developed apparatuses for inspecting unevenness in angular distribution of luminance of LCD display panels for example, utilizing a linear image sensor having charge coupled devices (the apparatus hereinafter referred to as CCD linear image sensor), as disclosed in Japanese Patent Early Publication 8-220014.
FIG. 7 shows a conventional luminance distribution measurement apparatus, which includes a linear image sensor 2L, LCD pixels 3, lines of pixels 3L, an LCD panel 4, a table 5 for moving the LCD panel 4 in x-direction, a light source 6, inspection data input device 7a, a LCD driver 8, a table drive control device 9, a light source control device 10, a display device 11 for displaying measurement data and results of the inspection, a data processing unit 12a, and a control unit 12b. 
In measuring the luminance of a LCD panel, the panel is illuminated by the light source 6. The CCD image sensors each receive light from corresponding pixels, transform it into an electric signal, and send it to the inspection data input device 7a. 
After the measurements of luminance distribution for one line of pixels, the table 5 is moved in the x-direction by the table drive control device 9 so that the linear image sensor 2L performs measurement of luminance of the pixels in the next line 3L. The inspection data input device 7a sends the measurement data to the data processing unit 12a, which stores, processes, inspects the data and displays the result of the inspection on the display device 11.
Generally, LCD panels have a characteristic that the luminance varies with viewing angle. The above mentioned known luminance measurement apparatus have drawbacks in that they fail to measure this luminance characteristic precisely. That is, in the inspection and/or analysis of an LCD panel, it simply measures the luminance in a predetermined direction, particularly in the direction normal to the panel.
The direction of the line of sight for a measurement apparatus looking at a pixel 3 on an LCD panel, or the direction of the beam of light radiated from the pixel 3, is represented by a polar coordinate (θ, φ), where θ is the vertical angle (hereinafter referred to as angle of incidence) between the normal axis passing through the pixel 3 and the line of sight, and φ is the azimuth angle with respect to a referential axis (referred to as x-axis) in the plane of the panel, as shown in FIG. 8. Thus, the angle of incidence θ is 0° for the line of sight normal to the LCD panel, while the angle of incidence is 90° for the line of sight parallel to the LCD panel. For the radiation emitted from the pixel 3, θ and φ are in the range 0≦θ≦90° and 0≦φ≦180°. In order to carry out inspection of the LCD panel, it is necessary to measure luminance over the entire angular domain.
However, a conventional sensor head (e.g. a image sensing device 2, a CCD camera) suffers from measurement errors made by the image sensors at the opposite ends of the device looking at the pixel at large angles θ, as shown in FIG. 9A. The errors will become larger when the LCD panel is moved for further measurement since the angle φ then increases.
The range of the angle of incidence θ that can be covered by the image sensor 2 could be extended by a lens 14 as shown in FIG. 9B. Since such lens has only a limited dimension, it still suffers similar errors at large angle of incidence θ and therefore the image sensor 2 would have a limited range for precise measurement of the luminance.
In order to precisely measure the luminance distribution for a given pixel up to about 90° in the angle of incidence θ, it is necessary to position the image sensor 2 at a large distance away from the pixel 3 as shown in FIG. 9C, and move the image sensor 2 perpendicularly to the radiation from the pixel 3.
In order to perform the measurement in a manner as described above and depicted in FIG. 9C, it is necessary to move the image sensor 2 along a circular orbit about the pixel after the image sensor 2 is positioned and fixed at a prescribed position relative to the pixel under measurement and then move the LCD panel in the x-direction, which requires a relatively complex mechanism for moving the image sensor 2 and the LCD panel, requiring much measurement time and a costly sophisticated machine.